The present invention relates to an X-ray image display apparatus for exposing a subject to an X-ray and thereby performing fluoroscopy and radiography on a subject region, and in particular to an X-ray image display apparatus in which a compensation filter and a collimator can be controlled so as to display an image satisfactorily on an image display device.
As shown in FIG. 1, a conventional X-ray image display apparatus of this kind includes a bed 2 for placing a subject 1 thereon, an X-ray tube 3 for exposing the subject 1 to an X-ray, an X-ray detector 4 disposed on the opposite side of the bed 2 from the X-ray tube 3 to convert an image of the X-ray transmitted through the subject 1 to a visible light image, a support 5 for supporting the X-ray tube 3 and the X-ray detector 4, a television camera 6 for scanning the visible light image supplied from the X-ray detector 4 and outputting a video signal, an A/D converter 7 for converting the video signal supplied from the television camera 6 to a digital signal, a display processor 8 for processing the digital signal supplied from the A/D converter 7 and converting the processed image data to a video signal, an image display device 9 for displaying the video signal inputted from the display processor 8 as an image, a compensation filter 10 disposed between the X-ray tube 3 and the subject 1 to partially an X-ray exposure dose, a filter control circuit 11 for manually adjusting the position of the compensation filter 10, a collimator 12 disposed on an output face of the X-ray tube 3 to partially interrupt the X-ray, and a collimator control circuit 13 for manually adjusting the collimator 12. The display processor 8 includes an image processor 14 for conducting processing such as frequency emphasis and subtraction on the digital signal supplied from the A/D converter 7, and a display circuit 15 for converting image data supplied from the image processor 14 to a video signal. In FIG. 1, numeral 16 denotes an X-ray controller for controlling the operation of the X-ray tube 3, and numeral 17 denotes a support controller for controlling driving of the bed 2 and the support 5.
In such an X-ray image display apparatus, an unnecessary part near the X-ray emitted from the X-ray tube 3 or a part where severe halation has occurred is interrupted by manually adjusting the collimator control circuit 13 while observing the image displayed on the image display device 9. As for a part having brightness close to that of halation, the brightness is lowered by adjusting the filter control circuit 11.
As an improvement to the conventional technique as shown in FIG. 1, a circuit for automatically controlling the filter control circuit 11 and the collimator control circuit 13 by using image data generated by the display processor 8 may occur to those skilled in the art. The circuit shown in FIG. 2 is a development of the conventional technique, and corresponds to an intermediate technique located between the conventional technique and the present invention.
In the X-ray image display apparatus shown in FIG. 2 with such an improvement added thereto, automatic control of the compensation filter 10 for removing unnecessary parts of the X-ray emitted from the X-ray tube 3 is exercised on the basis of a suitable control position calculated by the filter control circuit 11 by using image data taken in from the image processor included in the display processor 8. Representive examples of such calculation and control will now be described by referring to FIG. 3. FIG. 3 shows an output image region of the X-ray detector 4 including an X-ray image intensifier. The output image region is included in the scanning region of the television camera 6. The output image region is circular in shape. Therefore, the inside of a circle denoted by numeral 4 becomes an effective image region. The circular region is divided into a plurality of region blocks a, b, c, . . . , u. A representative value included in each region block is compared with a reference value. On the basis thereof, the filter control circuit 11 makes a calculation to determine whether the compensation filter 10 should be used or not. In general, it is desirable to conduct weighting in the central part and the peripheral part in the circular region and exercise control so as to form a satisfactory image in the central part. In case the X-ray passes outside the subject 1, i.e., the X-ray is directly incident upon the peripheral part of the X-ray detector 4, or in case a large quantity of contrast medium gathers in one place in subject 1 and hence the place can be judged to be a dark portion, it is also possible to exercise such control as to disregard the representative value of the region block of that part. A control signal based upon calculation in the filter control circuit 11 is sent to the compensation filter 10 to control the position of the compensation filter 10. By exercising such feedback control, a satisfactory image having reduced halation is obtained in fluoroscopy of a target part of the subject 1.
In recent years, advancements in image processing techniques have made it possible to expand and display moving pictures in real time and perform filtering on images in a video processing circuit. Expansion display been conventionally performed by changing the size of the image intensifier functioning as the X-ray detector 4. In angiography of the subject 1, however, a catheter and a guide wire have become very thin. In case expansion is performed only by stepwise changing the pickup range of the display screen of the image intensifier, the display area becomes narrower as the expansion ratio is increased. When the image is expanded, therefore, the catheter or wire might depart from the display range and be lost. Or even if the subject moves or the bed is slightly moved during display of an expanded image, the catheter or wire might depart from the display range and be lost. Thus, such expansion display has become uncapable of coping with such disadvantages. Therefore, expansion display using the display circuit 15 shown in FIG. 2 and digital processing has been put to use. In this case, an arbitrary area can be expanded or compressed at an arbitrary magnification owing to digital processing. In FIG. 4, the picked-up image area is represented by a square region E. FIG. 5 shows the display image area of the image display device 9. If, as an example, region blocks e, f, g, j, k, 1, o, p and q in the area included in the square region E shown in FIG. 4 are expanded by the display circuit 15, only the portion including the region blocks e, f, g, j, k, l, o, p and q is expanded and displayed on the screen of the image display device 9 as shown in FIG. 5. By using the image thus expanded and displayed, even a fine cathether can be easily manipulated.
In case expansion display using the display circuit 15 and digital processing is made in the image display in such an X-ray image diagnostic apparatus, the image in the area included in the square region E shown in FIG. 4 is taken in and the compensation filter 10 is controlled by the filter control circuit 11 by using representative values of respective region blocks e, f, g, j, k, l, o, p and q. Therefore, a satisfactory image is obtained as the entire image in the region 4. As for the expanded and displayed image portion shown in FIG. 5, however, a satisfactory display image is not obtained. The peripheral region shown in FIG. 4 is an area which is not observed. In the portion including the region blocks a, b, c, h, m, r, d, i, n, s, t and u, the subject 1 is thus subjected to unnecessary X-ray exposure. Therefore, the subject 1 is subjected to unnecessary exposure to the X-ray.
An object of the present invention is to provide an X-ray image display apparatus in which the position of a compensation filter or a collimator is controlled on the basis of display image data so as to display an image most satisfactorily.
Another object of the present invention is to provide an X-ray image display apparatus in which the position of a collimator is controlled on the basis of display image data so as to reduce exposure of a portion of the subject which is not displayed on the image to the X-ray.
In X-ray image display apparatuses, an X-ray image obtained by an X-ray detector is picked up by a television camera and the X-ray image thus picked up is subjected to image processing in a display processor and displayed on an image display device. However, the image actually displayed on the image display device is different from the X-ray image obtained by the X-ray detector. Even if an adjustment is made so as to optimize the X-ray image, therefore, it does not necessarily follow that the image displayed on the image 10 display device is optimized.
In accordance with the present invention, therefore, the apparatus includes a display area detector for detecting, on the basis of display image data processed by a display processor, a display area included in an X-ray image obtained by an X-ray detector and displayed on an image display device, and the position of a compensation filter or a collimator is controlled so as to optimize the X-ray image in the display area detected by the display area detector.
In accordance with another aspect of the present invention, the position of the collimator is controlled so as to expose only the part of the subject associated with the display area to the X-ray without exposing parts of the subject other than the display area detected by the display area detector to the X-ray.
In accordance with still another aspect of the present invention, a compensation filter for decreasing X-ray exposure dose is inserted for a portion brought to a halation state or a near-halation state and included in a display area detected by the display area detector, and the position of the compensation filter is controlled so as to make an image displayed on an image display device satisfactory. In particular, the X-ray directed to portions other than the display area is interrupted by a collimator to prevent the subject from being exposed to the X-ray. When an especially severe halation portion included in the display area cannot be sufficiently reduced by a compensation filter alone, the X-ray directed to that portion may be interrupted by inserting a collimator.
Operation of the X-ray image display apparatus thus configured will now be described. An image signal supplied from a display processor is inputted to a display area detector connected to the display processor. An image display area is detected by the display area detector. An image signal of the detected display area is sent to a filter control circuit. The compensation filter or collimator of the X-ray tube is controlled on the basis of the image signal of the display area by operation of this filter control circuit. As a result, the compensation filter or collimator can be controlled optimally.